Methylxanthines produced naturally by certain plant species include theophylline, theobromine and, most notably, caffeine. It is generally understood that theophylline and theobromine are precursors in the in vivo production of caffeine so that the relative abundance of these three methylxanthines in the plant will depend to some extent on the metabolic efficiencies of the particular plant and to further extent on the characteristic metabolism of the particular species of plant.
Theobromine, for example is produced by Theobroma cacao which is a valuable source of cocoa used in the food industry, usually in the production of chocolate confections. Cola acuminata and other Cola sp., which provide a source of cola flavorant, also produce theobromine. Sources of caffeine include Coffea arabica, C. robustas and other species of the coffee plant as well as the tea plant Cammellia thea and its relatives. Theophylline is believed to be present in each of these species but in less significant amounts than theobromine and caffeine. Extracts of these plants or, more commonly, of specific tissues of these plants e.g. coffee beans, tea leaves, etc., which are used in the preparation of foods or per se as beverages or beverage additives comprise not only the characteristic flavor factors, but also, in varying concentrations, the methylxanthines produced by the plants. For that reason, theophylline, theobromine and caffeine have been referred to as the dietary methylxanthines. The occurrence of dietary methylxanthines in foods and beverages and an assessment of their impact on health is described in The Methylxanthine Beverages and Foods, 1984, Alan R. Liss, Inc. New York.
Perhaps the most well known effect of a dietary methylxanthine is the stimulation of the central nervous system by caffeine which is experienced after consumption of coffee beverages. A similar stimulatory effect also results from consumption of foods and/or beverages prepared from theobromine-containing extracts such as cocoa-based foods and cola beverages. While theophylline is noted primarily as a muscle relaxant, it too may induce stimulation.
With the understanding that the methylxanthine effects may be undesirable, the coffee industry in particular has focused on developing processes which reduce the caffeine content of coffee extracts, at the same time retaining the pleasing taste and aroma of a beverage prepared from the treated extract.
Known processes for decaffeinating coffee focus on extracting caffeine either directly from the beans or from aqueous extracts thereof. In some processes, such as those disclosed in U.S. Pat. No. 4,547,378; EP No. 158,381, U.S. Pat. No. 4,515,695 and U.S. Pat. No. 4,505,940, caffeine is entrained in an organic solvent such as a halogenated hydrocarbon e.g. monochlorodifluoromethane or the carcinogen methylene dichloride, which is optionally further extracted to recover desired taste factors which may then be returned to the coffee extract after stripping the organic solvent. Solvent contamination of the end product, particularly with such solvents as the halogenated methanes and ethanes, is undesirable from a health viewpoint however.
An alternative process proposed in the art e.g. DE No. 3,445,502, relies on treatment with gaseous CO.sub.2 under super-critical conditions to decaffeinate coffee. Pressures above 200 bar are required, making this particular process economically unattractive. Extraction rates using this type of process can be enhanced using DMSO, according to U.S. Pat. No. 4,472,442, but the problem of solvent contamination must, again, be resolved.
Literature available on processes by which theobromine and theophylline are selectively extracted from foods and beverages or additives therefor are scant but it is believed that the same problems are encountered as are present in decaffeination processes.
Accordingly, it is an object of the present invention to provide a novel process for reducing the methylxanthine content of an aqueous solution. It is a further object of the present invention to provide a process for reducing the content of dietary methylxanthines present in foods and beverages or additives therefor.
It is a further, more specific object of the present invention to provide a decaffeination process effective to reduce the caffeine content of an aqueous coffee extract.